Free-flowing plural extrudates of polar ethylene interpolymers

ABSTRACT

Free-flowing plural extrudates of a polar ethylene interpolymer, and method of preparing the same. The extrudates are essentially coated with about 0.001-2 percent, by weight of the composition, fumed silica, preferably about 0.025-0.05 weight percent. The fumed silica has an average primary particle size of about 5-25 millimicrons, a surface area of about 200-250 m 2  /g, and is substantially amorphous and non-porous. The interpolymer has interpolymerized therein polar monomer, such as acrylic acid, n-butyl acrylate, vinyl acetate, or the like, in an amount so that the untreated extrudates have high block. The extrudates are treated by admixture with the silica or by contact with an aqueous dispersion of about 0.01-10 wt. % silica. When the interpolymer contains α,β-ethylenically unsaturated carboxylic acid, the extrudates are optionally surface neutralized with a base.

FIELD OF THE INVENTION

This invention relates to plural extrudates of ethylene interpolymerscontaining interpolymerized polar monomer which are treated to inhibittheir inherent high blocking tendency, and to a method of preparing thesame.

BACKGROUND OF THE INVENTION

Interpolymers of ethylene and one or more polar monomers, such asacrylic acid, methacrylic acid and vinyl acetate, are well known. Suchinterpolymers are commonly produced, sold and shipped in pelletizedform, or as plural extrudates. However, the high block, or the tendencyto stick or clump together, of pellets made of such interpolymers hasbeen a serious problem in transporting these products, both locally andto remote destinations, particularly with such interpolymers containinga relatively high proportion of interpolymerized polar monomer.

One attempt at solving this problem, when the polar monomer was anα,β-ethylenically unsaturated carboxylic acid such as acrylic acid, wasto surface neutralize the carboxyl groups of the interpolymer pellets orchips with a basic solution such as aqueous alkali metal hydroxide orcarbonate, ammonia, or aqueous amine, as described in U.S. Pat. No.3,753,965. However, over a period of time, typically about 3 months, theneutralizing cation migrated from the surface to the interior of thepellet or chip, reactivating the surface acid groups. In addition, anysurface distortion, such as might occur from erosion or breakage of thepellets during pneumatic conveying, or upon repeated heating andcooling, exposed unneutralized acid groups, resulting in an increasedtendency of the pellets to clump together. Moveover, if an excessivefraction of the acid groups were neutralized, properties of theinterpolymer, such as melt flow value, strength, stiffness, hardness,and softening point, were substantially adversely affected.

Another attempt was the employment of powdered anti-clumping agents suchas talc, calcium carbonate, and the like. When such materials wereeither intimately blended with the interpolymer or admixed with thepellets in an effective amount, the properties of the interpolymer, suchas stiffness and, in the case of aqueous dispersible grade resins,dispersibility, were substantially adversely affected. Moreover, it wasdifficult to accurately admix these additives in the desired proportionsand to obtain sufficient mixing to ensure that the surfaces of thepellets were adequately coated.

Other references which may be relevant to this application include: U.S.Pat. Nos. 3,595,827; 3,935,124; 2,882,254; 3,324,060; 3,901,992;3,916,058; 4,129,717; and U.S. Pat. No. 3,937,676.

SUMMARY OF THE INVENTION

Briefly, the invention is a free-flowing plural extrudate composition ofpolar ethylene interpolymers. The composition includes: (a) pluralextrudates of ethylene interpolymers having interpolymerized thereinethylene and polar monomer selected from the group consisting of:α,β-ethylenically unsaturated carboxylic acids having 3-8 carbon atomsand alkyl esters thereof, vinyl esters of carboxylic acids, andcombinations thereof; and (b) essentially surface coated on theextrudates, fumed silica having an average primary particle size betweenabout 5 and about 25 millimicrons, in an amount effective to impartsubstantially free-flowing characteristics to the extrudates.

The invention is also a method of preparing free-flowing pluralextrudates of polar ethylene interpolymers. The method includes thesteps of: (a) forming plural extrudates of ethylene interpolymers havinginterpolymerized therein ethylene and polar monomer selected from thegroup consisting of: α,β-ethylenically unsaturated carboxylic acidshaving 3-8 carbon atoms and alkyl esters thereof, vinyl esters ofcarboxylic acids, and combinations thereof; and (b) essentially surfacetreating the extrudates with fumed silica having an average primaryparticle size between about 5 and about 25 millimicrons and in an amounteffective to impart free-flowing characteristics to the extrudates. Thesurface treating is effected by admixing the fumed silica with theextrudates, or preferably by contacting the extrudates with an aqueousdispersion of the fumed silica during formation of the extrudates.

The composition of the present invention is free-flowing, retains itsfree-flowing characteristics over long periods, and substantiallyretains the physical properties of the untreated interpolymer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The plural extrudates of the invention may be formed by extruding themolten interpolymer through a die to form one or more strands,subsequently cooling the strands in a water bath, and finally choppingthe strands into pellets. The plural extrudates may also be, andpreferably are, formed by underwater pelletization in which the strandsare extruded directly into a water bath and cut at the die face. As usedherein, the term "plural extrudates" encompasses the interpolymer insimilar forms, which but for the high block of the interpolymer would befree flowing, such as, for example, rods, bricks, chips, chicklets, andthe like, whether formed by extrusion or other means.

The interpolymers from which the plural extrudates are formed containinterpolymerized ethylene and one or more polar monomers selected fromthe group consisting of: α,β-ethylenically unsaturated carboxylic acidshaving 3-8 carbon atoms and alkyl esters thereof, vinyl esters ofcarboxylic acids, and combinations thereof. Specific representativeexamples of such unsaturated carboxylic acids include acrylic acid,methacylic acid, ethacrylic acid, crotonic acid, isocrotonic acid,angelic acid, senecioic acid, tiglic acid, maleic acid, fumaric acid andthe like. Specific representative examples of alkyl esters of theseacids include the methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl,sec-butyl, and t-butyl esters and half-esters thereof. Specificrepresentative examples of such vinyl esters of carboxylic acids includevinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinylisobutyrate, vinyl valerate, vinyl isovalerate, and the like.

In addition, the interpolymers containing interpolymerizedα,β-ethylenically unsaturated carboxylic acid may be ionomers in which0-100 percent of the carboxyl groups are neutralized with a cation.Exemplary of such cations are: alkali metals such as sodium, potassium,lithium and the like; ammonium ions; and organic amines such as alkylamines, alkanol amines and the like.

The minimum amount of polar monomer interpolymerized in the ethyleneinterpolymer is not critical, except that there will usually be noadvantage in using the present invention unless the interpolymerizedpolar monomer content is such that the untreated plural extrudatesformed therefrom exhibit a blocking tendency. In general, a blockingtendency is observed when the interpolymerized polar monomer content isabout 4 mole percent or more.

In addition, the ethylene interpolymer may contain relatively minoramounts of additional polar or nonpolar monomers interpolymerizable withethylene, such as, for example, carbon monoxide, α-olefins such aspropylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene and thelike. Such additional monomers do not substantially reduce or increaseblocking tendency of the interpolymer.

The molecular weight of the interpolymers is not critical, but willnormally be sufficient to form plural extrudates. Depending on thespecific monomers, the interpolymers will typically have a melt flowvalue from about 0.1 to about 3000 dg/min per ASTM D-1238, condition190° C./2.160 kg (condition E), but may be more or less than this.Similarly, other properties of the interpolymer are not particularlycritical to the utility of the invention and will depend on the intendedend use and application. Such interpolymers and the methods of preparingthem and forming them into plural extrudates are well known.

The plural extrudates are essentially surface treated or coated withfumed silica in an amount effective to impart free-flowingcharacteristics thereto, preferably from about 0.001 to about 2 percentby weight of the composition, and more especially from about 0.025 toabout 0.05 percent by weight. Fumed silica is a well-known colloidalform of silica made by, for example, the combustion of silicontetrachloride or silicone tetrafluoride in a hydrogen-oxygen furnace.Fumed silica may also be chemically modified, for example, by alkylationor hydroxylation. The fumed silica useful in the present invention maybe either modified or unmodified, and has an average primary particlesize between about 5 and about 25 millimicrons, a surface area of fromabout 200 to about 250 m² /g, and is substantially amorphous andnon-porous. Such fumed silica is available commercially for example,from Cabot Corporation under the designations M-5, T-500 and N70-TS.

When the interpolymer includes interpolymerized α,β-ethylenicallyunsaturated carboxylic acid and is in a substantially non-ionomericform, or only partially ionomerized, the plural extrudates areoptionally surface-neutralized with cations to react the surfacecarboxyl groups to form salts. Exemplary cations include: alkali metalssuch as lithium, sodium, potassium and the like; ammonium ions; andorganic amines such alkyl amines, alkanol amines and the like. Suchsurface neutralization enhances the anti-blocking effect of the fumedsilica, and does not adversely affect the ability of the fumed silica tocoat the extrudate surfaces. In contrast to the known methods in whichsurface neutralization is the sole means of reducing block, however, itis not necessary to surface neutralize the extrudates to the extent thatthe properties of the interpolymer are adversely affected.

In preparing the free-flowing plural extrudates of the invention, pluralextrudates are formed from the interpolymer and essentially surfacetreated with the fumed silica. In one embodiment the surface treating iseffected by admixing the fumed silica with the plural extrudates in theaforementioned proportions with any suitable equipment, such as in a dryblender or by metering the fumed silica into the extrudate pneumaticconveying system.

In an especially preferred embodiment, the extrudates are contacted withan aqueous dispersion of hydrophilic fumed silica. The aqueousdispersion may contain the fumed silica in an amount of from about 0.01to about 10 percent by weight of the dispersion, preferably from about0.8 to about 1.1 percent by weight. Because of the size and nature ofthe fumed silica particles, it is not necessary to employ anydispersants, emulsifiers or similar additives, which may adverselyaffect the properties of the interpolymer, to prepare the aqueous fumedsilica dispersion. Exemplary of suitable hydrophilic fumed silica ishydroxylated fumed silica obtained from Cabot Corporation under thedesignation M-5.

When the plural extrudates are treated by contact with an aqueousdispersion of the fumed silica, they may be simply immersed in orsprayed with the dispersion and subsequently dried. Preferably, suchcontact is made by employing the aqueous silica dispersion as the quenchmedium in the conventional water bath for cooling the strands formedduring the formation of the plural extrudates or for cooling the pelletsformed during underwater pelletization. This method has the advantage ofeliminating any separate admixing step, and the readily prepared fumedsilica dispersion facilitates accurate measurement of the amount of thefumed silica coated on the pellets and ensures an adequate and moreuniform coating on substantially all of the pellets.

Optionally, the plural extrudates of the ethylene interpolymers havingα,β-ethylenically unsaturated carboxylic acid interpolymerized thereinmay also be surface neutralized by contact with a base. Such basesinclude alkali metal hydroxides, carbonates, and phosphates; ammonia;and organic amines. When the surface treating with fumed silica is bycontact of the extrudates with an aqueous dispersion of fumed silica,the dispersion may also contain the base, preferably in an amountsufficient so that the pH of the dispersion is from about 10 to about12. An especially preferred base is trisodium phosphate. It has beenfound that when the silica dispersion also contains a base, the wear onthe knife blades used to cut the interpolymer strands duringpelletization is generally reduced.

The plural extrudates treated in accordance with the invention aresubstantially free-flowing, even at the temperatures experienced instorage silos and hopper cars. In addition, the plural extrudates remainfree-flowing for longer periods of time and substantially resistreduction in their free-flowing characteristics upon deformation and/orbreakage during handling. It is believed that this improved retention ofthe free-flowing characteristic is due to a physical mechanism ratherthan a chemical mechanism as in surface neutralization techniquesheretofore employed. The fumed silica is believed to form a barrier ofdust on the surface of each pellet, providing a graphite-likelubricating action which allows the pellets to freely slide past eachother, rapidly coating any newly exposed surfaces. Moreover, thesubstantial absence of any change in the properties of the interpolymerobserved when the plural extrudates are put to an end use is believed toresult from the minute size of the fumed silica particles and therelatively small proportion of the fumed silica which is effective toimpart the free-flowing characteristics to the plural extrudates.

The practice and utility of the invention is illustrated by way of thefollowing examples:

EXAMPLE 1

A 500 g sample of pellets of an ethylene-acrylic acid interpolymercontaining 19.9 wt. % acrylic acid and having a melt flow value of 15dg/min per ASTM D-1238 condition 125° C./2.16 kg (condition B) wasplaced in a two liter beaker with an aqueous dispersion containing 0.47wt. % hydrophilic fumed silica obtained from Cabot Corporation under thedesignation M-5 (average particle size 10 millimicrons, surface area 200m² /g, chemical formula (SiO₂)₁₁₆₀₀ OH₁₀₀₀, bulk density 0.03 g/cc). Thepellets measured approximately 0.4 cm in diameter by 0.6 cm long. Afterabout three minutes of contact at ambient temperature (23° C.±1°), thedispersion was drained from the pellets. The treated pellets were spreadon an aluminum sheet, dried in a forced-draft oven at about 50° C., andallowed to cool to room temperature. The treated pellets contained about130 ppm fumed silica.

EXAMPLE 2

Pellets having the same characteristics as those treated in Example 1were treated as in Example 1, but with an aqueous dispersion containing0.95 wt. % of the M-5 fumed silica. The treated pellets contained about190 ppm fumed silica.

EXAMPLE 3

Pellets having the same characteristics as those treated in Examples 1-2were treated by admixing therewith about 250 ppm of the M-5 fumed anddry blending for about one hour in a conventional tumbler.

EXAMPLE 4

Pellets having the same characteristics as those treated in Examples 1-3were treated by admixing therewith about 500 ppm of the M-5 fumed silicaas in Example 3.

COMPARATIVE 1

Comparative 1 is a sample of untreated pellets having the samecharacteristics as those treated in Examples 1-4.

COMPARATIVE 2

Pellets having the same characteristics as those treated in Examples 1-4were treated as in Examples 1-2, but with an aqueous solution of 0.95wt. % trisodium phosphate containing no fumed silica.

The preparation of the above Examples and Comparatives is summarized inTable I.

                                      TABLE I                                     __________________________________________________________________________                        Fumed  Wt % Fumed Silica                                  Example/                                                                              Interpolymer                                                                              Silica Trade                                                                         In Treated                                                                              Treatment                                Comparative                                                                           Composition Designation                                                                          Composition                                                                             Method                                   __________________________________________________________________________    Example 1                                                                             80.1 wt. % Ethylene                                                                       M-5    ˜0.013                                                                            0.47 wt. %                                       19.9 wt. % Acrylic Acid      aq. dispersion                           Example 2                                                                             80.1 wt. % Ethylene                                                                       M-5    ˜0.019                                                                            0.95 wt. %                                       19.9 wt. % Acrylic Acid      aq. dispersion                           Example 3                                                                             80.1 wt. % Ethylene                                                                       M-5    ˜0.025                                                                            Dry blending                                     19.9 wt. % Acrylic Acid                                               Example 4                                                                             80.1 wt. % Ethylene                                                                       M-5    ˜0.05                                                                             Dry blending                                     19.9 wt. % Acrylic Acid                                               Comparative 1                                                                         80.1 wt. % Ethylene                                                                       --     --        None                                             19.9 wt. % Acrylic Acid                                               Comparative 2                                                                         80.1 wt. % Ethylene                                                                       --     --        Surface neutralized with                         19.9 wt. % Acrylic Acid      0.95 wt % aq. Na.sub.3 PO.sub.4          __________________________________________________________________________

Blocking Measurements

A drop test was used to determined the extent of pellet blocking. 3.5grams of pellets to be tested were placed in a 13.2 mm I.D.poly(methylmethacrylate) cylinder with an open end. A 12.7 mm O.D.poly(methylmethacrylate) rod was inserted in the cylinder on top of thepellets and a 488 g weight was placed on the rod pushing down on thepellets. (This weight was selected to simulate the force exerted onpellets at the bottom of a filled 6.1 m silo.) The whole apparatus washeated and maintained at 50° C. for a predetermined length of time.(This temperature was selected to simulate the estimated maximumtemperature in silos and hopper cars.) The cylinder was then removedfrom the oven, inverted and dropped at an initial height of 1.27 cm, andthen at heights sequentially increased by 1.27 cm, until the pelletswere dislodged completely. For each of the Examples 1-4 and Comparatives1-2, the average value of six tests is reported as the drop height inTable II.

                  TABLE II                                                        ______________________________________                                                     DROP TEST VALUE.sup.1 (cm)                                                    Aging Period at 50° C. (hrs).sup.2                        Comparative/Example                                                                          0.5        1.0      2.0                                        ______________________________________                                        Comparative 1  23 ± 8  25 ± 5                                                                              >63.5                                      Comparative 2  8 ± 3   11 ± 2                                                                              25 ± 13                                 Example 1      8 ± 3   16 ± 13                                                                             46 ± 15                                 Example 2      5 ± 2   3 ± 2 18 ± 10                                 Example 3      7 ± 2   7 ± 1 13 ± 10                                 Example 4      1 ± 1   2 ± 1 2 ± 1                                   ______________________________________                                         Notes for Table II:                                                           .sup.1 Error calculated as one standard deviation.                            .sup.2 As described in the paragraph entitled "Blocking Measurements".   

As seen in Table II, the treated pellets of Examples 1-4 showed a markedreduction in block in comparison with the untreated pellets (Comparative1), and with the exception of Example 1, a significant reduction inblock in comparison with the pellets treated only bysurface-neutralization (Comparative 2).

Physical Properties

The utility of the invention is further illustrated by the substantialabsence of any effect on the physical properties of the pellets treatedaccording to the invention in comparison with the untreated pellets.

                  TABLE III                                                       ______________________________________                                        Physical                                                                      Property     Com. 1  Com. 2  Ex. 1                                                                              Ex. 2                                                                              Ex. 3                                                                              Ex. 4                             ______________________________________                                        Melt Flow Value.sup.1                                                                      14.6    13.2    14.5 14.2 14.6 14.6                              (dg/min)                                                                      Ultimate Tensile                                                                           10.1    10.0    10.3 10.1 9.89 9.38                              Strength.sup.2                                                                (MN/m.sup.2)                                                                  Yield Strength.sup.3                                                                       4.72    4.90    4.69 4.62 4.69 4.48                              (MN/m.sup.2)                                                                  Elongation.sup.4 (%)                                                                       415     345     395  365  370  400                               Izod Impact.sup.5                                                                          0.16    --      --   --   0.16 0.16                              (N-m/cm notch)                                                                Tensile Impact.sup.6                                                                       41.0    39.5    42.9 39.1 40.3 30.7                              (N-m/cm.sup.2)                                                                Density (g/cm.sup.3)                                                                       0.955   0.957   0.955                                                                              0.956                                                                              0.956                                                                              0.956                             Hardness.sup.7 (Shore D)                                                                   40      --      --   --   40   45                                2% Secant Modulus.sup.8                                                                    0.269   --      --   --   0.262                                                                              0.262                             (N/m.sup.2)                                                                   Flex Modulus.sup.9                                                                         0.317   --      --   --   0.310                                                                              0.290                             (N/m.sup.2)                                                                   Vicat Softening                                                                            44      --      --   --   44   44                                Point.sup.10 (°C.)                                                     ______________________________________                                         Notes for Table III:                                                          .sup.1 Per ASTM D1238 condition 125° C./2.16 kg (condition B).         .sup.2 Per ASTM D638.                                                         .sup.3 Per ASTM D638.                                                         .sup.4 Per ASTM D638.                                                         .sup.5 Per ASTM D256-58.                                                      .sup.6 Per ASTM D1882.                                                        .sup.7 Per ASTM D2240.                                                        .sup.8 Per ASTM D790.                                                         .sup.9 Per ASTM D790.                                                         .sup.10 Per ASTM D1525.                                                  

As illustrated in Table III, the pellets treated with the fumed silicaexhibited a melt index similar to that of the untreated pellets, whereasthe surface-neutralized pellets exhibited a slight reduction. With theexception of the slightly lower ultimate tensile strength of Example 4,the physical properties of the treated pellets, regardless of thetreatment method, are similar to those of the untreated pellets.

Dispersibility

The utility of the invention is further similarly illustrated by theinsubstantial effect of treatment on the aqueous dispersibility ofdispersible grade resins as seen in Table IV.

                  TABLE IV                                                        ______________________________________                                                   DISPERSION PROPERTIES.sup.1                                                     Wt. %   Wt. % Non-                                                                              Ambient                                        Comparative/Example                                                                        Solids  Dispersible                                                                             viscosity (cp)                                                                         pH                                    ______________________________________                                        Comparative 1                                                                              24.9    0.09      110      8.85                                  Comparative 2                                                                              24.6    0.11      105      9.02                                  Example 1    24.9    0.09      120      8.90                                  Example 2    21.1    0.09      130      8.99                                  Example 3    24.6    0.08       90      8.90                                  Example 4    24.2    0.09      142      8.98                                  ______________________________________                                         Note for Table IV:                                                            .sup.1 Dispersed in 0.95 wt. % NH.sub.3 aqueous solution at 95° C.

Optical Properties

Pellets having the same characteristics as those treated in Examples 1-4were dry blended as in Examples 3-4 with 0, 0.2, 0.25, 1.0 and 3.0 phrof the M-5 fumed silica. The treated pellets were dispersed in 0.95 wt.% aqueous ammonia at 95° C. to obtain a dispersion of about 25 wt. %solids. The dispersions were cast into three-layer films with a number22 Meyer rod, and cured in a 90° C. oven for 5 minutes per layer. Thecast films were about 0.025 mm thick. The cast films were evaluated forclarity, gloss and haze, and the results are presented in Table V.

                  TABLE V                                                         ______________________________________                                        Fumed Silica (phr)                                                                        Clarity.sup.1                                                                          20° Gloss.sup.2                                                                  45° Gloss.sup.3                                                                Haze.sup.4                             ______________________________________                                        0           79       177       106     3.3                                    0.2         76       177       107     3.3                                    0.25        80       175       107     3.5                                    1.0         74       169       107     3.2                                    3.0         74       142       106     3.3                                    ______________________________________                                         Notes for Table V:                                                            .sup.1 Per ASTM D2457.                                                        .sup.2 Per ASTM D2457.                                                        .sup.3 Per ASTM D2457.                                                        .sup.4 Per ASTM D1003.                                                   

As seen in Table V, when the pellets are treated with an effectiveamount of the fumed silica according to the invention, the opticalproperties of film coatings remain substantially unchanged in comparisonwith those of the untreated pellets. At higher silica concentrations,gloss and clarity begin to decrease, and haze begins to increase.

Heat Seal Strength Properties

Kraft paper and 0.051-mm aluminum sheets were heat sealed with filmscast from the dispersions reported in Table IV. The films were castaccording to the procedure described for the films reported in Table V.The cast films were placed between substrate sheets and heat sealedface-to-face at two conditions: (1) at 93° C. for 1 second at 1.41kg/cm² ; and (2) at 116° C. for 5 seconds at 2.82 kg/cm². Strips 2.54 cmwide were peel tested with a tensiometer at 50.8 cm/min per ASTMD-903-49. The results are presented in Table VI.

                  TABLE VI                                                        ______________________________________                                                   Heat Seal Strength.sup.1 (kg/cm width)                             Example/Comparative                                                                        Paper.sup.2                                                                           Aluminum.sup.2                                                                          Paper.sup.3                                                                         Aluminum.sup.3                           ______________________________________                                        Comparative 1                                                                              0.643.sup.4                                                                           1.14      1.07.sup.4                                                                          2.04                                     Comparative 2                                                                              0.857.sup.4                                                                           1.64      1.05.sup.4                                                                          1.75                                     Example 1    0.821.sup.4                                                                           1.64      1.14.sup.4                                                                          1.79                                     Example 2    0.714.sup.4                                                                           1.50      1.18.sup.4                                                                          1.68                                     Example 3    0.750.sup.4                                                                           1.43      1.11.sup.4                                                                          1.82                                     Example 4    0.821.sup.4                                                                           1.36      1.11.sup.4                                                                          1.71                                     ______________________________________                                         Notes for Table VI:                                                           .sup.1 Per ASTM D903-49.                                                      .sup.2 Heat sealed at 93° C., 1.41 kg/cm.sup.2, 1 s dwell.             .sup.3 Heat sealed at 116° C., 2.81 kg/cm.sup.2, 5 s dwell.            .sup.4 Sample tear.                                                      

As seen in Table VI, the heat seal strength of films cast fromdispersions of the treated pellets was comparable to (even slightlyimproved in some instances) the heat seal strength of the untreatedpellets (Comparative 1) and the pellets only surface-neutralized(Comparative 2).

While we have desribed our invention above, many other variations willoccur to those skilled in the art. It is intended that all suchvariations which fall within the scope and spirit of the appended claimsbe embraced thereby.

We claim:
 1. A method of preparing free-flowing plural extrudates of apolar ethylene interpolymer, comprising the steps of:(a) forming pluralextrudates of an ethylene interpolymer having interpolymerized thereinethylene and polar monomer selected from the group consisting of:α,β-ethylenically unsaturated carboxylic acids having 3-8 carbon atomsand alkyl esters thereof, vinyl esters of carboxylic acids, andcombinations thereof; and (b) essentially surface treating saidextrudates with an effective amount of fumed silica having an averageprimary particle size between about 5 and about 25 millimicrons toimpart free-flowing characteristics thereto.
 2. The method of claim 1,wherein said amount of said fumed silica is from about 0.001 to about 2percent by weight of the free-flowing composition.
 3. The method ofclaim 2, wherein said surface treating includes admixing said fumedsilica with said extrudates.
 4. The method of claim 2, wherein saidsurface treating includes contacting said extrudates with an aqueousdispersion of said fumed silica.
 5. The method of claim 1, wherein saidaqueous dispersion contains from about 0.01 to about 10 percent, byweight of said dispersion, of said fumed silica.
 6. The method of claim1, wherein said interpolymer has interpolymerized thereinα,β-ethylenically unsaturated carboxylic acid having 3-8 carbon atoms,and wherein said method further comprises contacting said extrudateswith a base solution.
 7. The method of claim 6, wherein said base ispresent in said solution in an amount sufficient to provide a pH thereofof from about 10 to about
 12. 8. The method of claim 7, wherein saidbase is selected from the group consisting of:alkali metal hydroxides,alkali metal carbonates, alkali metal phosphates, ammonia, organicamines, and combinations thereof.
 9. The method of claim 7, wherein saidbase is trisodium phosphate.
 10. A method of preparing free-flowingplural extrudates of a polar ethylene interpolymer, comprising the stepsof:(a) extruding through a die to form a strand an ethylene interpolymerhaving interpolymerized therein ethylene and polar monomer selected fromthe group consisting of: α,β-ethylenically unsaturated carboxylic acidshaving 3-8 carbon atoms and alkyl esters thereof, vinyl esters ofcarboxylic acids, and combinations thereof; (b) cooling said strand bycontact thereof with an aqueous dispersion containing from about 0.01 toabout 10 percent, by weight of said dispersion, hydrophilic fumed silicahaving an average primary particle size between about 5 and about 25millimicrons and a surface area of from about 200 to about 250 m² /g,said fumed silica particles being substantially amorphous andnon-porous; and (c) cutting said strand into substantially free-flowingplural extrudates.
 11. The method of claim 10, wherein said interpolymerhas interpolymerized therein α,β-ethylenically unsaturated carboxylicacid having 3-8 carbon atoms, and wherein said dispersion contains abase.
 12. The method of claim 11, wherein said base is present in saiddispersion in an amount sufficient to provide a pH thereof of from about10 to about
 12. 13. The method of claim 12, wherein said base isselected from the group consisting of:alkali metal hydroxides, alkalimetal carbonates, alkali metal phosphates, ammonia, organic amines, andcombinations thereof.
 14. The method of claim 12, wherein said base istrisodium phosphate.
 15. The method of claim 12, wherein said cutting ofsaid strand is underwater in said dispersion at the face of said die.16. The method of claim 10, wherein said fumed silica is hydroxylated.17. The method of claim 10, wherein said aqueous dispersion containsfrom about 0.8 to about 1.1 percent by weight of said dispersion of saidfumed silica.
 18. A method of preparing free-flowing plural extrudatesof a polar ethylene interpolymer, comprising the steps of:(a) formingplural extrudates of an ethylene interpolymer having interpolymerizedtherein ethylene and polar monomer selected from the group consistingof: α,β-ethylenically unsaturated carboxylic acids having 3-8 carbonatoms and combinations thereof; and (b) contacting said extrudates withan aqueous dispersion containing from about 0.01 to about 10 percent, byweight of dispersion, hydroxylated fumed silica having an averageprimary particle size between about 5 and about 25 millimicrons and asurface area of from about 200 to about 250 m² /g, said fumed silicabeing substantially amorphous and non-porous, and a base in an amountsufficient to obtain a dispersion pH of from about 10 to about 12selected from the group consisting of: alkali metal hydroxides, alkalimetal phosphates, ammonia, organic amines and combinations thereof. 19.The method of claim 18, wherein said base is trisodium phosphate. 20.The method of claim 18, wherein said aqueous dispersion contains fromabout 0.8 to about 1.1 percent of said fumed silica by weight of saiddispersion.